Device, Method, and Scanner Correcting Document Image Using Correcting Mesh Constructed According to Vertical and Horizontal Boundaries and Adjusted Extended Filtered Lines

1. A device for correcting a document image, comprising: an extracting unit configured to extract first boundaries in a first direction of the document image, determine second boundaries in a second direction of the document image according to the first boundaries in the first direction, and extract lines in the first direction according to a content of the document image, where the first direction is one of a horizontal direction and a vertical direction of the document image, and the second direction is perpendicular to the first direction; a filtering unit configured to filter the lines in the first direction such that a difference between shapes of filtered lines and the first boundaries in the first direction is within a predetermined range; a constructing unit configured to extend the filtered lines to the second boundaries in the second direction according to the first boundaries in the first direction, adjust extended lines of the filtered lines according to adjacent lines adjacent to the filtered lines in the second direction and/or the first boundaries in the first direction, and construct a correcting mesh according to the first boundaries in the first direction and the second boundaries in the second direction and lines of which the extended lines have been adjusted; and a correcting unit configured to correct the document image according to the correcting mesh.

2. The device according to claim 1 , wherein the filtering unit comprising: a first filtering subunit configured to calculate a standard difference of second-direction coordinates of points on each line in the first direction, calculate a standard difference of second-direction coordinates of corresponding points on the first boundaries in the first direction of the document image, and further calculate a difference value between the standard difference of second-direction coordinates of the points on each line in the first direction and a maximum value of the standard differences of second-direction coordinates of the corresponding points on the first boundaries in the first direction, and remove lines where points of the difference values being greater than a predetermined first threshold are located.

3. The device according to claim 2 , wherein the filtering unit further comprising one of: a second filtering subunit configured to calculate a difference value between coordinates in the second direction of adjacent points on each line in the first direction, and remove lines where the points of the difference value between coordinates in the second direction being greater than a predetermined second threshold are located; and a third filtering subunit configured to calculate a distance between any two adjacent lines in the first direction, and remove a shorter line of the two adjacent lines in the first direction when the distance between the two adjacent lines in the first direction is greater than a predetermined third threshold.

4. The device according to claim 1 , wherein the constructing unit comprising: an extending unit configured to extend the filtered lines to the second boundaries in the second direction according to the first boundaries in the first direction; wherein a ratio of longitudinal distances of points on the extended lines to corresponding points on the first boundaries in the first direction of the document image is made to be equal to a ratio of longitudinal distances of endpoints of the filtered lines to corresponding points on the first boundaries in the first direction of the document image, to determine second-direction coordinates of the points on the extended lines, and determine first-direction coordinates of the points according to a straight line determined by corresponding points on the first boundaries in the first direction of the document image and the second-direction coordinates of the points.

5. The device according to claim 4 , wherein the constructing unit further comprising: an adjusting unit configured to adjust the extended lines of the filtered lines according to one of lines adjacent to the filtered lines in the second direction and the boundaries in the first direction, where all ratios between longitudinal distances of points on the adjusted extended lines to one of adjacent lines in the second direction and corresponding points on the first boundaries in the first direction of the document image are made to be equal to ratios between distances in the second direction of endpoints of the extended lines to adjacent lines in the second direction and corresponding points on the boundaries in the first direction of the document image, to determine second-direction coordinates of points on the adjusted extended lines; and the first-direction coordinates of the points are determined according to a straight line determined by corresponding points on the first boundaries in the first direction of the document image and the second-direction coordinates of the points.

6. The device according to claim 5 , wherein the constructing unit further comprising: a smoothing unit configured to perform smoothing processing to lines of which the extended lines have been adjusted.

7. The device according to claim 6 , wherein the constructing unit further comprising: a dividing unit configured to divide the document image into regions according to the first boundaries in the first direction and the second boundaries the second direction and smoothing-processed lines, wherein, one of: a position of a corresponding straight line of the smoothing-processed lines in the first direction in the region-divided document image is determined according to distances between points on the smoothing-processed lines and corresponding points on the first boundaries in the first direction of the document image and a distance between two boundaries in the first direction of the document image; and a position of a corresponding straight line of the smoothing-processed lines in the first direction in the region-divided document image is determined according to a distance between points adjacent to a ridge of the document image on the smoothing-processed lines and corresponding points on the first boundaries in the first direction of the document image and a distance between two boundaries in the first direction of the document image.

8. A scanner, comprising the device according to claim 1 .

9. A method for correcting a document image, comprising: extracting boundaries in a first direction of the document image, determining second boundaries in a second direction of the document image according to the first boundaries in the first direction, and extracting lines in the first direction according to a content of the document image; wherein the first direction is one of a horizontal direction and a vertical direction of the document image, and the second direction is perpendicular to the first direction; filtering lines in the first direction, so that a difference between shapes of filtered lines and the first boundaries in the first direction is within a predetermined range; extending the filtered lines to the second boundaries in the second direction of the document image according to the first boundaries in the first direction, adjusting extended lines of the filtered lines according to adjacent lines adjacent to one of the filtered lines in the second direction and the boundaries in the first direction, and constructing a correcting mesh according to the first boundaries in the first direction and the second boundaries in the second direction and lines of which the extended lines have been adjusted; and correcting the document image according to the correcting mesh.

10. The method according to claim 9 , wherein the filtering the line in the first direction comprising: calculating a standard difference of second-direction coordinates of points on each line in the first direction, calculating a standard difference of second-direction coordinates of corresponding points on the first boundaries in the first direction of the document image, and further calculating a difference value between the standard difference of second-direction coordinates of points on each line in the first direction and a maximum value of the standard differences of second-direction coordinates of the corresponding points on the first boundaries in the first direction, and removing lines where points of the difference values being greater than a predetermined first threshold are located.